1. Technical Field
The present invention relates to certain polymers that are useful as resists and that exhibit enhanced resistance to plasma and especially to Cl2/O2 plasma used in reactive ion etching. The present invention is concerned with the compositions as well as their use in lithography. For instance, the materials of the present invention are suitable for use in device and mask fabrication on optical, e-beam, x-ray and ion-beam lithography tools.
2. Background of Invention
In the manufacture of patterned devices and especially microelectronic devices, the processes of etching different layers that constitute the finished product are among the most crucial steps involved. One method widely employed in the etching process is to overlay the surface to be etched with a suitable mask.
The mask is typically created by imagewise forming a pattern of resist material over those areas of the substrate to be shielded from the etching. The resist is normally formed of a polymeric organic material. The pattern is formed by imagewise exposing the resist material to irradiation by lithographic techniques. The irradiation employed is usually x-ray, UV radiation, electron beam radiation or ion-beam radiation.
Radiation sensitive materials and/or compositions are either positive-acting (i.e. radiation solubilizable) or negative-acting (i.e. radiation insolubilizable or radiation crosslinkable). Positive-working (radiation) sensitive compositions are rendered soluble (or developable) by actinic radiation (deep-near UV, x-ray, electron-beam or ion-beam) and can be removed using selective developing solutions leaving unexposed areas intact. Negative-working (radiation) sensitive compositions are those which become insoluble upon exposure to actinic radiation. Selected solutions can dissolve and remove the unexposed areas of the composition while leaving the exposed portions intact. Development of such exposed materials yields negative tone images.
After the resist is developed forming the desired mask, the substrate and mask can be immersed in a chemical solution which attacks the substrate to be etched while leaving the mask intact. These wet chemical processes suffer from the difficulty of achieving well-defined edges on the etched surfaces. This is due to the chemicals undercutting the mask and the formation of an isotropic image. In other words, conventional chemical wet processes do not provide the resolution considered necessary to achieve optimum dimensions consistent with current processing requirements.
Moreover, such wet etching processes are undesirable because of the environmental and safety concerns associated therewith.
Accordingly, various so-called xe2x80x9cdry processesxe2x80x9d have been suggested to improve the process from an environmental viewpoint, as well as to reduce the relative cost of the etching. Furthermore, these xe2x80x9cdry processesxe2x80x9d have the potential advantage of greater process control and higher aspect ratio images. Also, when fabricating patterns having feature sizes below 350 nm, dry etching processes are necessary for profile control.
Such xe2x80x9cdry processesxe2x80x9d generally involve passing a gas through a container and creating a plasma in this gas. The species in this gas are then used to etch a substrate placed in the chamber or container. Typical examples of such xe2x80x9cdry processesxe2x80x9d are plasma etching, sputter etching, and reactive ion etching.
Reactive ion etching provides well-defined, vertically etched sidewalls.
One of the challenges in the fabrication of microelectronic devices and masks is to develop a resist which exhibits good lithographic performance as well as high dry etch resistance for subsequent pattern transfer into an underlying substrate. The dry etch chemistries include O2 currently used for antireflective coatings, Cl2/O2 currently used for chrome etching in mask fabrication, Cl2 based plasma for polysilicon etch, and fluorocarbon based plasmas such as CF4 for oxide etching. These plasmas are examples only and are not meant to limit the scope. Conventional novolak/diazonapthoquinone resists used for i-line lithography have to date exhibited excellent dry etch resistance to which other resist materials are compared.
Moreover, chemically amplified resists are employed extensively in the electronics industry. The chemically amplified resists are typically based on polyhydroxy styrene and other polymeric backbones that undergo deprotection when a photoacid generator, which is incorporated in the formulation, is exposed to actinic radiation.
The performance of these chemically amplified resists to withstand reactive ion etching in Cl2/O2 plasma requires improvement. Accordingly, a need exists to develop radiation sensitive compositions that provide improved dry etch resistance for use in mask fabrication (binary, attenuating phase shift masks, alternating phase shift masks) and for device fabrication.
The present invention provides compositions that are useful as resists and that are sensitive to imaging radiation that exhibits enhanced resistance to reactive ion etching. The compositions of the present invention typically exhibit enhanced resistance to reactive ion etching using, in particular, Cl2/O2 plasmas, Cl2 plasmas, O2 plasmas and fluorocarbon plasmas.
In particular, the polymers of the present invention are polymers comprising a polymeric backbone having grafted thereon at least one element selected from the group consisting of silicon, germanium and tin and mixtures thereof; and a protecting group.
The present invention also relates to a method for forming a pattern of a photoresist. The method comprises:
a) providing on a substrate a layer of a photoresist composition comprising a polymer having a polymeric backbone and grafted thereon at least one element selected from the group consisting of silicon, germanium, tin and mixtures thereof; and a protecting group;
b) imagewise exposing the layer to actinic radiation in a pattern to thereby cause a change in the solubility of the photoresist where exposed; and
c) developing the photoresist to thereby form the pattern.
A further aspect of the present invention relates to forming a pattern on a substrate. The method comprises:
a) providing a layer to be patterned on a substrate;
b) providing on the layer to be patterned a layer of a resist composition which comprises a polymer comprising a polymeric backbone having grafted thereon at least one member selected from the group consisting of silicon, germanium, tin and mixtures thereof; and a protecting group;
c) imagewise exposing the layer of resist composition to irradiation;
d) developing the resist to form the desired pattern; and
e) subjecting the layer to be patterned to reactive ion etching with the resist acting as a mask to thereby form the desired pattern on the substrate.
Still other objects and advantages of the present invention will become readily apparent by those skilled in the art from the following detailed description, wherein it is shown and described only the preferred embodiments of the invention, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, without departing from the invention. Accordingly, the description is to be regarded as illustrative in nature and not as restrictive.